Totally Tubular: Linear LEDs

With an urgent demand for energy efficiency, lighting continues to stake its claim as a solution. T8 and T5 fluorescents—both important evolutions in improved lamps and ballasts—have been landmark offerings. Now lighting installers have a new option: linear LEDs.

Recessed troffers and fluorescent lamps have successfully illuminated interior spaces for decades. Though LED tubes haven’t reached full parity with linear fluorescents, they are getting close. Their chief advantage has been their lumens-per-watt, sometimes bettering high-quality fluorescent lamps. They are also making gains in lighting quality, including glare, light distribution, visual appearance and color quality. Continued manufacturer breakthroughs are helping attract early adopters to linear LEDs.

“The lighting industry is currently undergoing a historic technology transition from traditional light sources, such as incandescent, HID, and fluorescent, toward LED,” said Jon Safran, director of Ambient Marketing (Metalux) for Cooper Lighting by Eaton. “As part of that, lighting manufacturers are working with different form factors, including linear LED modules, which continue to be a highly efficient and cost-effective method to deliver optimized LED solutions.”

Leading the charge in LED T8 testing and evaluation is Pacific Northwest National Laboratory (PNNL) in Richland, Wash. One of 10 U.S. Department of Energy (DOE) national laboratories, PNNL is operated by Battelle.

Naomi J. Miller is a designer/senior staff scientist at PNNL who evaluates linear LED products. PNNL’s latest report, “CALiPER Exploratory Study: Recessed Troffer Lighting” compares linear fluorescents against LED tubes in office and classroom settings. CALiPER is a DOE solid-state lighting testing program. The authors state: “As with standard reports, it is impossible for CALiPER to evaluate the full range of products available on the market. The selection process is intended to capture current trends, however, and the resulting observations are a valuable indicator of more widespread performance issues.” The authors encourage readers to compare their evaluations against benchmark information shared in other programs including LED Lighting Facts, Energy Star and the DesignLights Consortium (DLC).

In their testing, Miller explained how products are purchased anonymously and tested to simulate conditions contractors or operation managers face.

“If a manufacturer disagrees with our results or conclusions, we may retest to verify that our numbers are accurate. If the numbers stand, they stand,” Miller said.

In September 2012, the CALiPER study assembled a group of lighting designers, engineers and facility managers to observe and compare LED luminaires and their fluorescent counterparts. Twenty-four pairs of 2-by-2 and 2-by-4 troffers were tested for photometric and electrical performance, and they were installed in a mockup office space in Portland, Ore. Three of the pairs were T8 fluorescent benchmark products, 12 were dedicated LED troffers, five were fluorescent troffers modified for LED tube lamps, and four additional troffers were modified with LED retrofit kits. A commercial electrical contractor performed the modifications. The study concluded, “LEDs have not improved recessed troffers. But they have made them more efficient.” The report documents performance, illuminance, luminaire efficacy and many other factors.

Understanding LED tubes

The installation of this new LED product was an important part of the study. Like LED lighting in general, the installation of linear LEDs isn’t exactly plug-and-play. If there ever were a case for electrical contractors (ECs) to pause and read installation directions, this would be it.

“There are five different ways to wire up these tubes,” Miller said. “They are single-end wired; double-end wired; double-end wired with additional wire between pins on two ends of the tube; remote driver; and no wiring change when the lamp operates on fluorescent sockets wired for existing instant-start fluorescent ballast.”

For the EC who modified the study’s fluorescent fixtures for LED, the instructions for removing ballasts and rewiring sockets for LED T8 lamps were easier to understand, but it was more work and more time-consuming than installing an LED retrofit kit.

“The contractor told us no manufacturer should expect ECs to rewire sockets,” Miller said. “You basically want to swap one socket out with a new one.”

As is the case with all LED lighting, driver standardization is an issue for LED linear tubes. Study participants stated the need “to improve dimming drivers to reduce flicker and provide smoother dimming performance with lower minimum output levels.” Some manufacturers’ drivers are better than others in this regard.

Installation and safety

Miller said that, once you have rewired your lighting fixture for an LED T8, you can’t put a fluorescent lamp back in or any other LED tube with different wiring.

“You’ll trip circuits or worse,” Miller said.

She stressed that installers must rewire every fixture for the lighting type they are using and then label those fixtures so mistakes aren’t made when, say, an LED T8 needs to be replaced. A small number of LED tube manufacturers are offering products that fit right into the fluorescent sockets, operating on the same instant-start fluorescent ballast.

“That makes installation of the T8 LEDs very easy because no rewiring is necessary in the luminaire, but an electrician must check to ensure the existing ballast is instant-start, not rapid-start,” Miller said. “You don’t want someone putting back in a fluorescent T8 when the fixture has been rewired for LED T8.”

Miller stressed that a contractor could end up violating the factory warranty, NRTL certification, or National Electrical Code if the installation and placement of proper identification stickers to transfer responsibility aren’t properly done.

Some manufacturers are making conversions easy. CREE Inc. has removed the compatibility concern between the replacement tube and the fixture wiring.

“We eliminated the use of the two stem sockets,” said Jeff Hungarter, product portfolio manager, Commercial Lighting, at Cree. “Through our retrofit approach, our lights feature a quick connect wire to snap in place so you don’t have to rewire the socket.”

Lighting variables

Other variables must be considered when comparing LED tubes to fluorescents. Light distribution is one of them. While fluorescent fixtures accept light emitted from the full 360 degrees of the tube, the light output for LED tubes is directional. Equipped with varying degrees of plastic face, some tubes distribute a narrow beam of light (usually 120 degrees or less), some a medium beam, and others a wide beam (typically 140 degrees or more). A buyer should ask manufacturers what they offer.

“This angle of light emission changes the photometrics of the fixture,” Miller said. “The wider the angle of light emission, the closer the luminaire performance will be to that of the original fluorescent lamp. T8 LED tubes with narrower angles might be better for illuminating a very specific space such as a jewelry case but not a good choice for broader light disbursement for an office space.”

Miller suggested that, if you are swapping fluorescent T8 for the efficiency of LED tubes but need a wide light distribution, look for tubes with a wider beam angle and a larger luminous surface. “You also need to look at your lumens per watt delivered by the lamp and luminaire together, not just the lamp itself,” she said.

Also, while many LED tubes are coated for diffused light, some are not, which can lead to glare, depending on installation location.

“The unit brightness of the exposed LEDs can be very high,” Miller said. “Parabolic fixtures are a problem, in this case, as the tubes are very bright and offer a narrow spread of light. The glare potential of the diffused tubes, however, is comparable to fluorescents.”

Cost is a bottom-line question. Is it a wash when you compare the higher purchase and installation cost of LED tube lighting against the benefit of their promised longer life? It depends.

“The cost of the electrical retrofit/installation, the hours of use [the longer the better], and the local electric rates all influence payback time,” Miller said. “Today, there are a handful of LED T8 products that better the life of high-performance fluorescents, which themselves offer anywhere from 30,000 to 80,000 hours of lamp life with efficacies around 100 [lumens per watt]. Some dedicated light LED troffers offer fixture efficacy that is higher than the fluorescent lamp alone.”

“The road block to LED adoption is justifying a bigger purchase versus a lower cost alternative. Buyers often contemplate waiting for LED costs to go down. The counter argument is the cost of waiting is the cost of sacrificing energy savings,” Cree’s Hungarter said.

Consulting the manufacturer

Knowing the LED tube market and working with the manufacturer is well worth the time for ECs and customers alike. Miller suggested the EC get a copy of a photometric test, including a report on the bare lamp performance and its operation within a typical lighting fixture. (see www.ecmag.com/photometric report to learn how to read one.)

“The tube affects the performance of the luminaire,” Miller said. “You need to know its light distribution, how much light it will produce throughout the space [including the walls] and how much power it will draw.”

She recommended getting product samples.

“Customers should tell the EC how they want to install the LED T8s; four fixtures in a row,” Miller said. “They should also ask for a time estimate and cost for rewiring the fixtures. The EC can then accurately advise how difficult one configuration of lighting might be to wire versus another approach. Remember, if you are using the LED tubes that operate on fluorescent ballasts, you still have to replace the ballast when it goes.”

Further study

PNNL is currently following up on its 2013 study.

“We are evaluating over 50 tube styles in hopes of matching up what tubes in their beam width capacity are best suited for what fixtures,” Miller said.

For instance, she explained, if one is looking to use LED T8 in a traditional two-by-four troffer with a K12 prismatic lens as opposed to a parabolic louver troffer, the study will attempt to provide a usage/selection guide, so customers understand what tubes are best for the needed light distribution.

“While it is more than a simple lighting swap out, this is a new product that continues to improve,” Miller said. “It may do the best job for what you need, but do your homework.”